Modified bitumens were developed in Europe during the late 1960's for roofing applications and found a market in the United States during the 1980's. These products are an important part of the roofing industry and are produced as a continuous sheet on a roofing line and are later cut down to individual pieces and wound in rolls of various lengths. Subsequent to laying on a roof, they are top coated with coatings that provide energy efficacy and reflectivity.
With prior art white reflective coatings problems have occurred in maintaining roof surface reflectivity. Reflectivity decreases the most during the first year of a roof's life. After three years, the rate that reflectivity declines is typically less significant. Changes in reflectivity are primarily related to changes with the coating itself (e.g., coating erosion or cracking) and/or minimally related to accumulation of particulate matter (e.g., dirt) from atmospheric fallout. Depending on the geographic exposure and how well roof surfaces drain, keeping roof surfaces white and preventing premature failure from cracking and peeling can be a significant challenge and result in major maintenance expenditures for owners. Maintaining reflectivity may involve regular cleaning, regular restoration of reflective coatings, and regular application of biocides and/or fungicides. There remains a need for improved coatings with greater reflectivity, energy efficacy and durability.
Prior art coatings are applied directly to granule-surfaced modified bitumen roof membranes on new roof systems or as restorative coatings. Examples of such coatings are found in U.S. Pat. No. 6,060,555. However, granules are difficult to coat because of their rough, uneven surface areas. Moisture and air pockets can be trapped under the coating and lead to blisters or pinholes in the cured coating. Consequently, application of a compatible primer to the granule surface before coating application is required. Inconsistent coverage and potential cracking of areas where the coating is applied too heavily are additional problems related to application of previous coatings. Hence, there is a need for a method for top coating application that consistently results in uniform thicknesses of the coating.
Prior art coatings require application to the roofing membrane subsequent to placement of the modified bitumen membranes. Most coatings are recommended to be applied a few days, and sometimes as much as 60 days later on AAP modified products, after installation of the roofing membrane, which extends the time needed for prompt completion of the roofing project. Application requires special equipment such as a pressure washer, paddle mixer and spray rig as well as personal protective equipment. Pressure washing removes embedded dirt, chalking, carbon black and poorly adhered material. A paddle mixer is required as the coating must be completely stirred to ensure proper polymer dispersion because the solids may have settled at a container's bottom. Hence, there is a need for coating compositions that can be easily and effectively applied without the need for special equipment.
Certain coatings, such as acrylic coatings develop strength and adhesion as they cure during installation. When an acrylic coating is applied, two physical changes must occur: water must evaporate from the applied coating film for initial drying and acrylic polymers must fuse together for final cure. Consequently, for application purposes multiple thin coats promote water evaporation, polymer dispersion, and help eliminate pinholes, voids or thin spots.
Application of water-based acrylic coatings is influenced by changing weather conditions. Virtually all parts of North America have some application limitations as a result of cold weather, daily rainstorms, high humidity and/or fog, or reduced daylight hours during winter. Rain on an uncured coating will cause a partial or total coating run-off. Problems occur when an acrylic coating is specified on a construction project without regard to the time of year the coating is to be installed.
Additionally, two or more successive coats of the coating are often necessary. Further, the drying of the coating is influenced by weather conditions. Cold temperatures and lack of sunlight decrease the freshly applied coating's evaporation. Water in the coating film closest to the membrane diffuses through slowly. Coatings exposed to water conditions during the drying or coating period may soften, lift and debond from the surface. This often requires cleaning of the surface and reapplication of the coating. The final cure takes place during the first few weeks after application and is essential to the coating's long term performance. Wet weather and cooler temperatures inhibit final cure and may inhibit proper fusing. Consequently, acrylic coating applications cannot be attempted on roofing projects from late fall to early spring in most North American areas.
Film laminate coatings cannot be directly applied to asphaltic compounds because of inter alia difficulties due to heat sensitivities of the film, potential for delamination of the film caused by exudation of oil from modified bitumen membranes, and discoloration of the film due to exudation of oil. U.S. Pat. No. 5,096,759 discloses a membrane containing a laminated top aluminum foil surface and a bottom bitumen coating surface. However, foil materials typically have very smooth surfaces, which may provide insufficient surface area for binding, and therefore could delaminate from the surface of the asphaltic compound after cooling of the roofing membrane. Moreover, use of a thin layer of aluminum can cause the surface film laminate to fail by erosion or damage due to traffic. Conversely, use of a thicker foil increases cost in addition to posing other problems such as the product becomes very rigid and difficult to handle. Importantly, foil will not meet Energy Star® requirements.
Hence, there is a need for new and improved laminated coating compositions that may be applied in-plant during manufacture of the roll roofing membrane. In particular, a coating composition is needed that is reflective, energy efficient (meeting today's Energy Star® criteria) as well as durable and easy to apply, and which is not vulnerable to the effects of moisture and cold temperatures during the curing process.
Roofing granules, both natural and artificially color-coated granules, are extensively used in roll roofing and asphalt shingle compositions. The roofing granules are typically embedded in the asphalt coating on the surface of an asphalt-impregnated felt base material, the granules thus forming a coating that provides a weather-resistant exterior roofing surface. In addition to weather-resistance, the color-coated granules also provide an esthetic effect observable with respect to the coating compositions; the appearance of the granules is of major marketing interest. For this reason, a pigmented color coating is ordinarily applied to the base mineral granules. In addition to pigments, the granule coatings may contain additives such as algaecides to help extend the color and appearance of the roofing material. Roofing granules are generally used in asphalt shingle or in roofing membranes to protect asphalt from harmful ultraviolet radiation.
Roofing granules typically comprise crushed and screened mineral materials, which are coarse and are subsequently coated with a binder containing one or more coloring pigments, such as suitable metal oxides. The binder can be a soluble alkaline silicate that is subsequently insolubilized by heat or by chemical reaction, such as by reaction between an acidic material and the alkaline silicate, resulting in an insoluble colored coating on the mineral particles. The granules are then employed to provide a protective layer on asphaltic roofing materials such as shingles, and to add aesthetic values to a roof.
Pigments for roofing granules have usually been selected to provide shingles having an attractive appearance, with little thought to the thermal stresses encountered on shingled roofs. However, depending on location and climate, shingled roofs can experience very challenging environmental conditions, which tend to reduce the effective service life of such roofs. One significant environmental stress is the elevated temperature experienced by roofing shingles under sunny, summer conditions, especially roofing shingles coated with dark colored roofing granules. Although such roofs can be coated with solar reflective paint or coating material, such as a composition containing a significant amount of titanium dioxide pigment, in order to reduce such thermal stresses, this utilitarian approach will often prove to be aesthetically undesirable, especially for residential roofs.
Further, traditional granules used on roofing substrates such as modified bitumen products and built up roofing products are single-coated, coarse and large. Therefore, once a top coating is applied to these granules once adhered to the roofing products, the reflectivity provided by these granules is not sufficient to pass ASTM standards, and other high standards required by certain states. Thus, there is a continuing need for roofing granules that provide increased solar heat reflectance to reduce solar absorption.